The next generation of environmentally friendly commodity plastics is being developed based on two essential design strategies. First, the polymers are derived from sustainable feedstocks based on biomass. Second, the polymers are readily degradable in the environment on a timescale measured in months or years.
Poly(lactic acid) (PLA) currently stands as the most commercially successful biorenewable synthetic thermoplastic. The persistence of this aliphatic polyester in a landfill, however, can rival that of traditional petroleum-based thermoplastics. The indiscriminate esterases generally responsible for ester hydrolysis are sparse in a landfill and, thus, PLA degradation is optimal only in the biotic, warm, and oxygen-rich conditions of compost. One route to alleviating this detriment is through the incorporation of the acetal functional group (e.g., —OCH2O—) into the main-chain of polymeric architectures. Like biomass, this functional group is oxygen-rich and the central carbon's oxidation state (O) matches the average oxidation state of photosynthetic building blocks (e.g., glucose, C6H12O6). Moreover, nature uses this functional group to connect the glucose units of earth's most abundant polymer, cellulose. Important to polymer chain scission, the acetal functional group is readily hydrolyzed under acidic aqueous conditions. Thus, degradation is congruous with the conditions of a landfill, where surface bacteria and fungi expel acidic metabolites that percolate via rainfall to the lower, abiotic, anoxic (low oxygen) regions, which display a lower pH.
Ring-Opening Polymerization (ROP) is a widely employed technique for the conversion of cyclic monomers to linear polymers. Large cyclic acetals that are amenable to ROP, however, are generally not feasible for large-scale and efficient production. Hence, a general and effective method for the production of polyacetals by an acetal metathesis reaction is desirable.